Method of making a metal grating in a waveguide and device formed

ABSTRACT

A method of making a grating in a waveguide includes forming a waveguide material over a substrate, the waveguide material having a thickness less than or equal to about 100 nanometers (nm). The method further includes forming a photoresist over the waveguide material and patterning the photoresist. The method further includes forming a first set of openings in the waveguide material through the patterned substrate and filling the first set of openings with a metal material.

BACKGROUND

Waveguides are used to control a propagation of light from one elementto another. Waveguides are used in image sensors, opticalcommunications, opto-electric circuits, spectrum analysis devices aswell as other technologies. Diffraction gratings are used in waveguidesto separate different wavelengths of a light beam or to combinedifferent wavelengths into a single light beam.

A transmission grating separates an incoming light beam into componentwavelengths by refracting the incident light beam. An angle ofrefraction is determined in part by the wavelength of the componentwavelength. Similarly, the transmission grating combines light ofdifferent wavelengths into a single output light beam by refracting theincident light so that multiple wavelength input are combined into thesingle output light beam.

A reflecting grating separates the incoming light beam into componentwavelengths by reflecting the incident light beam. An angle ofreflection is determined in part by the wavelength of the componentwavelength. Similarly, the reflective grating combines light ofdifferent wavelengths into the single output light beam by reflectingthe incident light so that multiple wavelength input are combined intothe single output light beam.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments are illustrated by way of example, and not bylimitation, in the figures of the accompanying drawings, whereinelements having the same reference numeral designations represent likeelements throughout. It is emphasized that, in accordance with standardpractice in the industry various features may not be drawn to scale andare used for illustration purposes only. In fact, the dimensions of thevarious features in the drawings may be arbitrarily increased or reducedfor clarity of discussion.

FIG. 1 is a flow chart of a method of making a metal grating in awaveguide in accordance with one or more embodiments;

FIGS. 2A-2F are cross sectional views of a waveguide structure duringvarious stages of production in accordance with one or more embodiments;

FIG. 3 is a top view of a waveguide structure in accordance with one ormore embodiments;

FIG. 4 is a cross sectional view of a waveguide structure in accordancewith one or more embodiments;

FIG. 5 is a top view of a waveguide structure in accordance with one ormore embodiments; and

FIG. 6 is a top view of a waveguide structure in accordance with one ormore embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are examples and are not intended to belimiting.

FIG. 1 is a flow chart of a method 100 of making a metal grating in awaveguide in accordance with one or more embodiments. Method 100 beginswith operation 102 in which a waveguide material is formed over asubstrate. In some embodiments, the waveguide material is formed on thesubstrate by a chemical vapor deposition (CVD) process, a physical vapordeposition (PVD) process, an atomic layer deposition (ALD) process, anepitaxial process, or another suitable formation process. In someembodiments, an insulating layer (not shown) is formed between thewaveguide material and the substrate. In some embodiments, theinsulating layer is formed by a CVD process, a PVD process, an ALDprocess, an epitaxial process, or another suitable process.

A thickness of the waveguide material over the substrate is less than orequal to about 100 nanometers (nm). In some embodiments, the thicknessof the waveguide material over the substrate is less than or equal toabout 75 nm. The thickness of the waveguide material in method 100 isreduced with respect to other methods due to the ability of method 100to produce highly reflective gratings with increased critical dimension(CD) control in comparison with other methods.

FIG. 2A is a cross-sectional view of a waveguide structure 200 followingoperation 102 in accordance with one or more embodiments. Waveguidestructure 200 includes a substrate 202 and a waveguide material 204 overthe substrate. A thickness of waveguide material 204 is equal to or lessthan about 100 nm. In some embodiments, the thickness of waveguidematerial 204 is less than about 75 nm.

Substrate 202 is used to support waveguide material 204. In someembodiments, substrate 202 is a dielectric layer or printed circuitboard (PCB). In some embodiments, substrate 202 includes activecircuitry such as photo detectors, light emitters, transistors or othersuitable active circuitry. In some embodiments, substrate 202 includesan interconnect structure between the active circuitry and waveguidematerial 204. In some embodiments, substrate 202 includes silicon,silicon-on-insulator (SOI), silicon with defective crystallinity,diamond or other suitable materials.

Waveguide material 204 is over substrate 202. Waveguide material 204 iscapable of allowing propagation of a wide spectrum of wavelengths. Insome embodiments, the wavelengths include visible light, ultra-violet(UV) light, infrared (IR) light or other suitable wavelengths. In someembodiments, wavelength material 204 includes a dielectric material suchas silicon dioxide (SiO₂), silicon carbide (SiC), carbon nitride (CN),silicon oxynitride (SiON), silicon nitride (SiNx), or another suitabledielectric material. In some embodiments, wavelength material 204includes BLACK DIAMOND™ by Applied Materials.

In some embodiments, an insulating layer (not shown) is betweensubstrate 202 and waveguide material 204. In some embodiments, theinsulating layer is a transparent material. In some embodiments, theinsulating layer includes SiO₂, SiC, CN, SiNx, silicon oxycarbide(SiOC), or other suitable materials. In some embodiments, the insulatinglayer includes a same material as waveguide material 204. In someembodiments, the interconnect structure for active circuitry insubstrate 202 is formed in the insulating layer. In some embodiments,the insulating layer is a multi-layer structure. In some embodiments,the insulating layer is a single layer. In some embodiments, a thicknessof the insulating layer ranges from about 100 nm to about 10,000 nm.

Returning to FIG. 1, method 100 continues with operation 104 in which aphotoresist is formed over the waveguide material. In some embodiments,the photoresist is formed by a spin-on process, a PVD process or anothersuitable formation process. One of ordinary skill in the art willappreciate that various photoresist thicknesses are able to be achievedby using different types of photoresist materials or by varying the spinspeed used during formation of the photoresist. In some embodiments, thephotoresist includes a positive photoresist material. In someembodiments, the photoresist includes a negative photoresist material.In some embodiments, additional layers such as anti-reflective (AR)coatings, hard mask layer, or other suitable layers are formed betweenthe photoresist and the waveguide material.

FIG. 2B is a cross-sectional view of a waveguide structure 200 followingoperation 104 in accordance with one or more embodiments. Waveguidestructure 200 includes a photoresist 206 over waveguide material 204. Insome embodiments, photoresist 206 includes a positive photoresistmaterial. In some embodiments, photoresist 206 includes a negativephotoresist material. In some embodiments, using a positive photoresistreduces thermal expansion or shrinkage in comparison with a negativephotoresist. The reduced thermal expansion or shrinkage helps to improveCD control. A thickness of photoresist 206 ranges from about 100 nm toabout 500 nm.

Returning to FIG. 1, method 100 continues with operation 106 in whichthe photoresist is patterned. In some embodiments, the photoresist ispatterned using a photolithography process. In some embodiments, thephotolithography process uses UV light to pattern the photoresist. Thephotolithography light causes exposed portions of the photoresist tobecome more soluble to a developer solution, while portions of thephotoresist remain insoluble to the developer solution. The developersolution is then used to remove the more soluble areas leaving thepatterned photoresist with a structure having openings therein.

In some embodiments, multiple sets of openings are formed duringoperation 106. In some embodiments, at least one set of openings has adifferent period from another second of openings. In some embodiments,each set of openings formed in the photoresist are formedsimultaneously. In some embodiments, at least one set of openings isformed subsequent to at least another set of openings.

FIG. 2C is a cross-sectional view of a waveguide structure 200 followingoperation 106 in accordance with one or more embodiments. Waveguidestructure 200 includes openings 208 and 210 formed in photoresist 206.In some embodiments, openings 208 have a different period than openings210. In some embodiments, openings 208 have a same period as openings210. A period of openings 208 and openings 210 is selected to correspondto a desired diffraction wavelength.

A diffraction grating is able to be defined based on the equation:

mλ=d(sin α+sin β)   (1)

Wavelength=2*N*Pitch/m

where m is the order of diffraction, λ is the wavelength beingdiffracted, d is the grating pitch, α is the angle of incidence, and βis the angle of diffraction, and N is an integer. A wavelength to bediffracted and a diffraction order are predetermined by a user. Theangle of incidence is adjustable based on the orientation of openings208 and openings 210. A designer is then able to determine the gratingpitch so as to diffract the predetermined diffraction order of thepredetermined wavelength of light based on the incident angle determinedby the orientation of openings 208 and 210. In some embodiments, agrating pitch of openings 208 and openings 210 ranges from about 100 nmto about 1000 nm.

In some embodiments, openings 208 and openings 210 have a width rangingfrom about 10 nm to about 300 nm. The width of openings 208 and 210determines a width of gratings formed using the openings. If the widthof openings 208 and openings 210 is too great, the material of thegratings will absorb a significant amount of incident light therebyreducing an overall intensity of light exiting the grating. If the widthof openings 208 and openings 210 is too small, the grating will not beable to efficiently diffract incident light.

Returning to FIG. 1, method 100 continues with operation 108 in whichopenings are formed in the waveguide material. Openings are formed inthe waveguide material through the patterned photoresist. In someembodiments, the openings in the waveguide material are formed by anetching process, such as a dry etching process, a wet etching process, areactive ion etching (RIE) etching process, a plasma-assisted etchingprocess or another suitable material removal process. In someembodiments, the photoresist is removed during operation 108. That is,the material removal process used to form the openings in the waveguidematerial simultaneously removes the material of the patternedphotoresist. In some embodiments, the patterned photoresist is removedin a process subsequent to operation 108.

FIG. 2D is a cross-sectional view of waveguide structure 200 followingoperation 108 in accordance with one or more embodiments. Waveguidestructure 200 includes openings 208 and 210 extending throughphotoresist 206 and waveguide material 204. A period of openings 208 andopenings 210 in waveguide material 204 is substantially the same as theperiod of period of openings 208 and openings 210 in photoresist 206. Inthe embodiment of FIG. 2D, photoresist 206 is removed subsequent toforming openings 208 and openings 210 in waveguide material 210.

In some embodiments, openings 208 and openings 210 extend completelythrough waveguide material 204. In some embodiments, openings 208 andopenings 210 extend less than completely through waveguide material 204.In some embodiments, a depth of openings 208 and openings 210 inwaveguide material 204 independently range from about 20 nm to about 100nm.

Returning to FIG. 1, method 100 continues with operation 110 in which ametal material is formed in the openings in the waveguide material. Insome embodiments, the metal material is formed by electroplating,sputtering, PVD, ALD or another suitable formation process. The metalmaterial fills the openings in the waveguide material and extends over atop surface of the waveguide material. In some embodiments, the metalmaterial includes copper, aluminum, alloys thereof or other suitablemetal materials. In some embodiments, the metal material is formed overthe patterned photoresist. In some embodiments, the photoresist isremoved prior to forming the metal material in the openings. In someembodiments, the patterned photoresist material is removed by an etchingprocess, an ashing process, or other suitable removal processes.

FIG. 2E is a cross-sectional view of waveguide structure 200 followingoperation 110 in accordance with one or more embodiments. Waveguidestructure 200 includes a metal material 212 over waveguide material 204.Metal material 212 fills openings 208 to form a first grating 214 andfills openings 210 to form a second grating 216. Metal material 212 isover a top surface of waveguide material 204. In the embodiment of FIG.2E, photoresist 206 was removed prior to forming metal material 212.

In some embodiments, a barrier layer is formed between each portion ofmetal material 212 filing each opening of openings 208 and openings 210.In some embodiments, the barrier layer includes titanium (Ti), tantalum(Ta), titanium nitride (TiN), tantalum nitride (TaN) or other suitablebarrier layer material.

Returning to FIG. 1, method 100 continues with operation 112 in whichthe metal material is planarized. In some embodiments, the metalmaterial is planarized using a chemical mechanical polishing (CMP)process. In some embodiments, the metal material is planarized using anetching process, a grinding process or another suitable material removalprocess. In some embodiments, the patterned photoresist is removedduring operation 112. Following operation 112, a top surface of themetal material is substantially coplanar with the top surface of thewaveguide material.

FIG. 2F is a cross-sectional view of waveguide structure 200 followingoperation 112 in accordance with one or more embodiments. Waveguidestructure 200 includes metal material 212 having a top surfacesubstantially coplanar with the top surface of waveguide material 204.Operation 112 removes metal material 212 over the top surface ofwaveguide material 204. As a result, first grating 214 and secondgrating 216 have a substantially flat top surface coplanar with the topsurface of waveguide material 204.

One of ordinary skill in the art would recognize that additionaloperations are able to be added to method 100 and an order of operationsare able to be adjusted to form a final product.

FIG. 3 is a top view of a waveguide structure 300 in accordance with oneor more embodiments. Waveguide structure 300 includes a first waveguide302 extending in a first direction and configured to allow light topropagate along a length of the first waveguide. Waveguide structure 300further includes a second waveguide 304 extending in a second directiondifferent from the first direction. Second waveguide 304 is configuredto allow light to propagate along a length of the second waveguide.Waveguide structure 300 further includes a third waveguide 306 extendingin the second direction spaced from second waveguide 304. Thirdwaveguide 306 is configured to allow light to propagate along a lengthof the third waveguide. Waveguide structure 300 further includes afourth waveguide 308 extending in the second direction spaced fromsecond waveguide 304 and third waveguide 306. Fourth waveguide 308 isconfigured to allow light to propagate along a length of the fourthwaveguide. In some embodiments, the first direction is perpendicular tothe second direction. Waveguide structure 300 further includes a firstgrating 310 located at an intersection of first waveguide 302 and secondwaveguide 304. Waveguide structure 300 further includes a second grating320 located at an intersection of first waveguide 302 and thirdwaveguide 306. Waveguide structure 300 further includes a third grating330 located at an intersection of first waveguide 302 and fourthwaveguide 308.

Waveguide structure 300 is configured to operate as either a beamsplitter or a beam combiner. Waveguide structure 300 is capable ofoperating as a beam splitter by having a multi-wavelength beam of lightpropagate along first waveguide 302. As the multi-wavelength beam oflight is incident on first grating 310, a first wavelength λ1 splits offfrom the multi-wavelength beam of light and propagates along secondwaveguide 304. The first wavelength λ1 is determined by a period offirst grating 310. In a non-limiting example, the pitch of first grating310 is 425 nm, an angle of incidence of the multi-wavelength beam oflight on the first grating is 45-degrees, and a reflection angle is45-degrees. Based on the diffraction equation Eq. (1), first grating 310splits off a first order of the first wavelength λ1 equal to 850 nm.

Similarly, second grating 320 and third grating 330 split off differentwavelengths depending on a period of the second grating and the thirdgrating, respectively. In some embodiments, first grating 310 has adifferent pitch than at least one of second grating 320 or third grating330. In some embodiments, each of first grating 310, second grating 320and third grating 330 have a different pitch.

Waveguide structure 300 is capable of operating as a beam combiner byhaving a light beam with a specific wavelength propagate along at leasttwo of second waveguide 304, third waveguide 306 or fourth waveguide308. A corresponding grating at an intersection with first waveguide 302directs the light from the at least two waveguides along the firstwaveguide to form a multi-wavelength beam of light.

In some embodiments, a number of gratings is more or less than three. Insome embodiments, a number of waveguides is more or less than four. Insome embodiments, the first direction and the second direction isdifferent from 90-degrees.

FIGS. 4 is cross sectional view of waveguide structure 300 taken alongline A-A of FIG. 3 in accordance with one or more embodiments. Firstgrating 310, second grating 320 and third grating 330 are embedded infirst waveguide 302. In some embodiments, a barrier layer separatesfirst waveguide 302 from a material of each of first grating 310, secondgrating 320 and third grating 330.

FIG. 5 is a top view of a waveguide structure 500 in accordance with oneor more embodiments. Waveguide structure 500 includes a first waveguide502 extending in a first direction and configured to allow light topropagate along a length of the first waveguide. Waveguide structure 500further includes a second waveguide 504 extending in a second directiondifferent from the first direction. Second waveguide 504 is configuredto allow light to propagate along a length of the second waveguide.Waveguide structure 500 further includes a third waveguide 506 extendingin a third direction different from the first direction and the seconddirection. Third waveguide 506 is spaced from second waveguide 504.Third waveguide 506 is configured to allow light to propagate along alength of the third waveguide. Waveguide structure 500 further includesa fourth waveguide 508 extending in a fourth direction different fromthe first direction, the second direction, and the third direction.Fourth waveguide 508 is spaced from second waveguide 504 and thirdwaveguide 506. Fourth waveguide 508 is configured to allow light topropagate along a length of the fourth waveguide. First waveguide 502,second waveguide 504, third waveguide 506 and fourth waveguide 508intersection one another at an intersection structure 510. Waveguidestructure 500 includes a grating 550 located at a surface ofintersection structure 510 configured to receive light propagating alongeach of first waveguide 502, second waveguide 504, third waveguide 506and fourth waveguide 508.

Grating 550 has a prismatic shape. In some embodiments, grating 550 hasa triangular prismatic shape. In some embodiments, grating 550 has adifferent shape. Grating 550 is formed in a similar manner as thatdescribed above with respect to method 100 with a variation in shape ofthe opening in a waveguide material.

Waveguide structure 500 is configured to operate as either a beamsplitter or a beam combiner. Waveguide structure 500 is capable ofoperating as a beam splitter by having a multi-wavelength beam of lightpropagate along first waveguide 502. As the multi-wavelength beam oflight is incident on grating 550, a first wavelength λ1 splits off fromthe multi-wavelength beam of light and propagates along second waveguide504. The first wavelength λ1 is determined by a period of grating 550 aswell as the angle of incident and the angle of diffraction as shownabove in Eq. (1).

Waveguide structure 500 is capable of operating as a beam combiner byhaving a light beam with a specific wavelength propagate along at leasttwo of second waveguide 504, third waveguide 506 or fourth waveguide508. Grating 550 at intersection structure 510 directs the light fromthe at least two waveguides along first waveguide 502 to form amulti-wavelength beam of light.

FIG. 6 is a top view of a waveguide structure 600 in accordance with oneor more embodiments. Waveguide structure 600 includes a first waveguide602 extending in a first direction and configured to allow light topropagate along a length of the first waveguide. Waveguide structure 600further includes a second waveguide 604 extending in a second directiondifferent from the first direction. Second waveguide 604 is configuredto allow light to propagate along a length of the second waveguide.Waveguide structure 600 further includes a third waveguide 606 extendingin a third direction different from the first direction and the seconddirection. Third waveguide 606 is spaced from second waveguide 604.Third waveguide 606 is configured to allow light to propagate along alength of the third waveguide. Waveguide structure 600 further includesa fourth waveguide 608 extending in a fourth direction different fromthe first direction, the second direction, and the third direction.Fourth waveguide 608 is spaced from second waveguide 604 and thirdwaveguide 606. Fourth waveguide 608 is configured to allow light topropagate along a length of the fourth waveguide. First waveguide 602,second waveguide 604, third waveguide 606 and fourth waveguide 608intersection one another at an intersection structure 610. Waveguidestructure 600 includes a transmission grating 650 located inintersection structure 510 configured to receive light propagating alongeach of first waveguide 602, second waveguide 604, third waveguide 606and fourth waveguide 608.

Waveguide structure 600 is configured to operate as either a beamsplitter or a beam combiner. Waveguide structure 600 is capable ofoperating as a beam splitter by having a multi-wavelength beam of lightpropagate along first waveguide 602. As the multi-wavelength beam oflight is incident on transmission grating 650, a first wavelength λ1splits off from the multi-wavelength beam of light and propagates alongsecond waveguide 604. The first wavelength λ1 is determined by a periodof transmission grating 650 as well as the angle of incident and theangle of diffraction as shown above in Eq. (1).

Waveguide structure 600 is capable of operating as a beam combiner byhaving a light beam with a specific wavelength propagate along at leasttwo of second waveguide 604, third waveguide 606 or fourth waveguide608. Transmission grating 650 at intersection structure 610 directs thelight from the at least two waveguides along first waveguide 602 to forma multi-wavelength beam of light.

One aspect of this description relates to a method of making a gratingin a waveguide. The method includes forming a waveguide material over asubstrate, the waveguide material having a thickness less than or equalto about 100 nanometers (nm). The method further includes forming aphotoresist over the waveguide material and patterning the photoresist.The method further includes forming a first set of openings in thewaveguide material through the patterned substrate and filling the firstset of openings with a metal material.

Another aspect of this description relates to a method of making agrating in a waveguide. The method includes forming a waveguide materialover a substrate, the waveguide material having a thickness less than orequal to about 100 nanometers (nm) and forming a photoresist over thewaveguide material. The method further includes forming a first set ofopenings in the waveguide material having a first pitch. Forming thefirst set of openings includes forming a first set of photoresistopenings in the photoresist, and etching the waveguide material throughthe first set of photoresist openings. The method further includesforming a second set of openings in the waveguide material having asecond pitch. Forming the second set of openings includes forming asecond set of photoresist openings in the photoresist, and etching thewaveguide material through the second set of photoresist openings. Themethod further includes filling the first set of openings and the secondset of openings with a metal material.

Still another aspect of this description relates to a waveguidestructure including a substrate and a waveguide material over thesubstrate, wherein the waveguide material has a thickness less than orequal to about 100 nanometers (nm). The waveguide structure furtherincludes a first metal grating having a first pitch in the waveguidematerial. A depth of the first metal grating is less than the thicknessof the waveguide material, and a top surface of the first metal gratingis substantially coplanar with a top surface of the waveguide material.

It will be readily seen by one of ordinary skill in the art that thedisclosed embodiments fulfill one or more of the advantages set forthabove. After reading the foregoing specification, one of ordinary skillwill be able to affect various changes, substitutions of equivalents andvarious other embodiments as broadly disclosed herein. It is thereforeintended that the protection granted hereon be limited only by thedefinition contained in the appended claims and equivalents thereof.

What is claimed is:
 1. A method of making a grating in a waveguide, themethod comprises: forming a waveguide material over a substrate, thewaveguide material having a thickness less than or equal to about 100nanometers (nm); forming a photoresist over the waveguide material;patterning the photoresist; forming a first set of openings in thewaveguide material through the patterned substrate; and filling thefirst set of openings with a metal material.
 2. The method of claim 1,wherein forming the photoresist comprises forming a positivephotoresist.
 3. The method of claim 1, further comprising planarizingthe metal material so that a top surface of the metal material issubstantially coplanar with a top surface of the waveguide material. 4.The method of claim 1, wherein patterning the photoresist comprises:performing a photolithography process on the photoresist; and etchingthe photoresist to form a first set of photoresist openings in thephotoresist corresponding to the first set of openings in the waveguidematerial.
 5. The method of claim 1, further comprising forming a secondset of openings in the waveguide material through the patternedsubstrate.
 6. The method of claim 5, wherein forming the second set ofopenings in the waveguide material comprises forming the second set ofopenings in the waveguide material having a different pitch than fromthe first set of openings in the waveguide material.
 7. The method ofclaim 5, wherein patterning the photoresist further comprises etchingthe photoresist to form a second set of photoresist openings in thephotoresist corresponding to the second set of openings in the waveguidematerial.
 8. The method of claim 7, wherein the first set of photoresistopenings in the photoresist is formed simultaneously with the second setof photoresist openings in the photoresist.
 9. The method of claim 1,further comprising forming an insulation layer between the substrate andthe waveguide material.
 10. The method of claim 1, further comprisingremoving the photoresist prior to filling the first set of openings inthe waveguide material.
 11. The method of claim 1, further comprisingremoving the photoresist following filling the first set of openings inthe waveguide material.
 12. A method of making a grating in a waveguide,the method comprises: forming a waveguide material over a substrate, thewaveguide material having a thickness less than or equal to about 100nanometers (nm); forming a photoresist over the waveguide material;forming a first set of openings in the waveguide material having a firstpitch, wherein forming the first set of openings comprises: forming afirst set of photoresist openings in the photoresist, and etching thewaveguide material through the first set of photoresist openings;forming a second set of openings in the waveguide material having asecond pitch, wherein forming the second set of openings comprises:forming a second set of photoresist openings in the photoresist, andetching the waveguide material through the second set of photoresistopenings; and filling the first set of openings and the second set ofopenings with a metal material.
 13. The method of claim 12, wherein thefirst set of openings in the waveguide material is formed simultaneouslywith the second set of openings in the waveguide material.
 14. Themethod of claim 12, further comprising removing the photoresistsimultaneously with etching the waveguide material through the secondset of photoresist openings.
 15. The method of claim 12, wherein formingthe second set of openings in the waveguide material comprises formingthe second pitch different from the first pitch.
 16. The method of claim12, further comprising planarizing the metal material so that a topsurface of the metal material is substantially coplanar with a topsurface of the waveguide material.
 17. The method of claim 12, whereinfilling the first set of openings and the second set of openingscomprises filling the first set of openings and the second set ofopenings with copper, aluminum, or alloys thereof.
 18. A waveguidestructure comprising: a substrate; a waveguide material over thesubstrate, wherein the waveguide material has a thickness less than orequal to about 100 nanometers (nm); a first metal grating having a firstpitch in the waveguide material, wherein a depth of the first metalgrating is less than the thickness of the waveguide material, and a topsurface of the first metal grating is substantially coplanar with a topsurface of the waveguide material.
 19. The waveguide structure of claim19, wherein the waveguide material comprises silicon dioxide (SiO₂),silicon carbide (SiC), carbon nitride (CN), silicon oxynitride (SiON),silicon nitride (SiNx).
 20. The waveguide structure of claim 19, furthercomprising a second metal grating having a second pitch different formthe first pitch.